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pulse customer base of around 150, with several product designs having reached production. These are typically from sectors such as small-cell basestation makers, where experienced RF designers were among the first to exploit the chip’s capabilities. However, Ebrahim Busherhi, Lime CEO and instigator of Myriad-RF, believes that the ease-of-use of configurable RF technology should be a platform on which a diverse array of new product concepts can emerge, and that the open community approach may be the way to further that aim. Myriad-RF boards use field programmable RF (FP-RF) transceivers to operate on all mobile broadband standards – LTE, HSPA+, CDMA, 2G – including all regional variants; and any wireless communications frequency between 0.3 and 3.8GHz. This includes the regulated, licensed bands and unlicensed/whitespace spectra. Lime has also beta-launched the Myriad-RF community website and forum, www.myriadrf. org. This resource will also house the board design files and example projects with how-to guides and the ability for users to contribute extra content. All of the design files will be open and downloadable – the CAD environment is KiCad (www.kicadpcb. org). Designs hosted on myriadrf.org will initially come from Lime and close partners, but Lime seeks to increase involvement and design contribution from the general RF design community – both hobbyists and professional system designers. Azio’s Myriad-RF 1 board measures approximately 5x5cm, uses a 5V power supply and is software configurable to operate from 300MHz to 3.8GHz and on 2G, 3G and 4G communication networks. Pre-built boards will initially retail for $299 or less: Busherhi hopes this will reduce over time. A distribution network is already in place for pre-built boards and components with Azio Electronics and Eastel already participating. Links to all available pre-built boards can be found on the Myriad-RF board pages. Busherhi mentions ideas such as the possibility of using an FPGA-based baseband board together with a Myriad- RF card, which would provide an environment that would be totally programmable from one end of the signal chain to the other. The Myriad board is, he says, “a simple board with simple connections – you don’t have to worry about the RF, it becomes part of the design.” Although Lime Microsystems has an established customer base in areas such as military radio and defence, and in cellular basestations, Busherhi is emphatic that he does not want to restrict activities to any niche sectors; “When we got (our chip) in production, we went broad-market right away, selling it in any quantity to any customer.” With Myriad-RF, he hopes to expand that base in the open model. - by Graham Prophet Lime Microsystems, www.limemicro.com Multi-cell balancing to increase battery pack performance Linear Technology’s LTC3300-1 is the company’s latest IC that addresses the problem of managing the state-of-charge of a multi-cell battery, such as the battery packs in electric vehicles or hybrids (Evs/HEVs). The underlying problem is that cells are never identical and as they age, capacities degrade, and by different amounts in different cells. Unless managed, the capacity of the pack is set by the performance of the lowest-capacity cell. Linear’s latest chip balances the cell state of charge in a series-connected battery stack. Many existing solutions carry out balancing by reducing the charge on higher-charged cells to match the lowest; this optimises the performance of the pack but is inefficient, as the marginal energy is dumped in resistive discharge. LTC3300-1 goes beyond dissipative passive balancing solutions, efficiently transferring charge to or from adjacent cells in order to bring mismatched cells into balance within the stack. Benefits claimed are faster charging and extending the run time and usable lifetime of the battery stack. You would use the LTC3300-1 in a battery management system (BMS) for series-connected Li-Ion or LiFePO4 batteries. Proposed architectures for active cell balancing include switched circuit arrangements with capacitive or inductive elements, in which some energy is taken from the highest-level cell and passed along the series-connected chain to the lowest. This needs many conversion steps to move a significant amount of charge. Or, there are single-transformer approaches in which the entire pack is switched across, in effect, the primary of a transformer, and the secondary is selectively connected back to the weakest cell. This also requires long balancing times. w ww.edn-europe.com MARCH 2013 | EDN Europe 11


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